Precast concrete modular building panel

ABSTRACT

A precast modular panel suitable for forming at least a portion of a wall or other part of a building comprising a layer of lightweight high strength concrete.  The lightweight aggregates comprise scoria to impart strength to the concrete, in cooperation with especially selected pumice to provide water resistance and high insulative properties, along with chopped fiberglass to enhance the structural strength, so that the lightweight concrete possesses strengths fully comparable to those of many concretes for structural uses. The insulative properties of the lightweight concrete contrasts very favorably to those of other lightweight concretes, and with conventional structural concrete. The panel may be so constructed as to require no subsequent decorative finishing.

BACKGROUND

1. Field of the Invention

Broadly, the present invention relates to the use of concrete as amaterial for constructing buildings, and more particularly toconstruction of buildings using precast panels of concrete. With stillmore particularity, the invention relates to the use of modular panelsto make up at least a portion of the walls of buildings, the panelsbeing precast of concrete comprising lightweight aggregates and strengthenhancers.

2. Prior Art

Heretofore, precast panels for the construction of buildings,particularly for the walls thereof, have utilized structural concrete toattain the structural strength required to withstand handling loads andloads imposed by the building structure. However, the use of structuralconcrete, which normally comprises heavy aggregates such as gravel andthe like, has caused the panels to be excessively heavy, so thathandling the installation has been both expensive and laborious, alsorequiring unnecessarily expensive heavy handling equipment. Further,such panels have required much finishing work after installation intothe building to provide the aesthetic effects often desired. Such panelshave, additionally, been difficult to work with, since fasteningbuilding objects thereto requires the use of rock drills and the like.Further, they have often required the addition of insulating materialsthereto. The resulting final building walls have accordingly beencomposite structures wherein the panel has comprised only one part, sothat the total expense of such panels has seriously compromised thepotential economic advantages inherent to mass produced panels.

In attempts to overcome the aforesaid disadvantages of the use ofstructural concrete for panels, much work has been done with lightweightaggregates in the concrete for use in panels. However, concretes madefrom these lightweight aggregates, which include vermiculite, perlite,scoria, pumice, expanded shale, cinders and others, have in mostinstances possessed less than desirable structural strength, or haveeven been excessively low in structural strength. Concretes comprisingvermiculite and perlite in particular have largely been limited tostrength below 1000 pounds per square inch so that their uses havelargely been as insulating fillers, with other structural componentsbeing provided to carry the imposed loads. Concretes comprising pumiceor scoria exhibit somewhat higher structural strengths, while beingsomewhat more dense. However, the strength of the pumice and scoriaconcretes have been largely limited to 1000 to 3000 p.s.i., still lessthan desirable for many structural uses.

Another problem with the use of lightweight aggregates comprisingconcrete for precast builing panels is the tendency of such concretes tobe pervious to water, so that exposed panels tend to be damaged byweather excessively fast. Thus, although a concrete comprising scoria,for example, as the principal aggregate may, marginally, possesssufficient structural strength, such concrete is normally unacceptablysusceptibile to moisture and water.

While expanded shale, clay, or slate can be used as a lightweightaggregate to produce acceptable structural strength while remainingsufficiently impervious to water, such concretes are comparativelyexpensive to construct, since these aggregates require extended dryingin kilns and the like, or sintering, and careful handling of theaggregate, generally with specialized equipment, to achieve therequisite strengths.

Still another important consideration for modular panels making up thewalls of buildings has been their insulating properties. Resistance toheat flow through the panels should be at a high level to minimize thecost of subsequent heating and cooling the resulting structure.Generally, the concretes exhibiting high strength have been less thandesirable as insulating structures. Structural concrete, for instance,is not in itself an effective insulator for the wall of a building.Generally, even the above mentioned more expensive lightweight concretesfall short of desired insulating properties. Accordingly, insulatinglayers of other materials have of necessity been added to the panelsused in the construction of buildings. These have often comprisedcellular plastic materials, or even cork, wood and the like, and havecontributed additional material and installation expense. Attempts havealso been made to construct panels comprising layers of concrete forstrength and layers for high insulative properties, the layers beingcast one upon the other. However, these panels have often beenunsatisfactory because the layers tend strongly to separate, before orafter installation into a building, so that such panels often cannot beso used.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION

The present invention eliminates or substantially alleviates theaforesaid disadvantages of the prior art by providing lightweightconcretes, panels constructed thereof, and associated methods. Theconcretes are light in weight, have entirely adequate structuralstrength for use in modular panels for building construction, and have ahigh degree of insulation to obviate the necessity of adding insulatinglayers. The lightweight concretes of the present invention furtherexhibit entirely adequate resistance to moisture and water and arehighly fire resistant.

The modular panels in accordance with the present invention may beconstructed by simple mass production techniques and may be installedwith a minimum of equipment and labor, requiring little or no finishingwork after installation into the walls or other parts of a building,since surfaces of selectable textured appearance are achieved during thecasting of the panels. The inventive lightweight concrete compriseslightweight aggregates and structural additives which cooperate in theconcrete to produce a highly useful combination of high insulatingproperties in a panel which can be constructed economically by massproduction methods.

With the foregoing in mind, it is a primary object of the presentinvention to provide a precast modular panel suitable for forming aportion of a wall or other suitable part of a building, said panel beinglight in weight, high in strength, highly resistant to water, and highlyresistant to the flow of thermal energy therethrough.

Another paramount object of the invention is to provide a lightweightconcrete having unusually low density and high structural strength in awater resistant concrete.

A still further paramount object of the invention is to provide a methodof producing panels entirely satisfactory for use in the construction ofbuilding walls thereof, said method being economical, and requiringminimum amounts of labor and time.

Another paramount object of the invention is to provide differentlycomprised concretes selectively of high strength and of high insulativeperformance which may be cast in layers, one upon the other withoutseparating one from the other after their cure together to form a panelor other object.

A still further object of the invention is to provide a lightweightconcrete comprising lightweight aggregates conforming with Federalstandards for lightweight aggregates for use in housing construction.

A still further object of the invention is to produce a precast modularpanel having surface finishes such that further finishing for decorativepurposes is not required.

Another object of the invention is to provide a precast modular buildingpanel requiring no addition of insulative material.

Still another object of the invention is to provide a precast concretemodular wall panel wherein electrical conduits and cooperatingelectrical outlet boxes are provided in the panels so as to communicatewith similar boxes and conduits in adjacent panels and with the upperedges of the panels so that no electrical channels need be installed inthe building walls after the building is constructed of the panels.

A still other object of the invention is to provide a precast modularpanel carrying provisions for attachment to similar panels and to thefoundation, window frames, door frames and the like of the building.

A still further object of the invention is to provide a precast modularpanel construction method whereby available molds and forms are utilizedto the optimum degree.

A still further object of the invention is to provide a precast modularpanel construction method whereby a single large mix of lightweightconcrete may be used in construction of a plurality of such panels.

Still further objects and advantages of the present invention will beapparent from the detailed description of the illustrated embodiments ofthe invention, made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective, partially broken, representation of a modularbuilding panel in accordance with the principles of the invention.

FIG. 2 is a perspective representation of a mold into which theinventive concrete and suitable insulating concrete are poured to form aprecast concrete modular building panel in accordance with theprinciples of the invention.

FIG. 3 is a cross-sectional representation of the mold of FIG. 2, takenalong line 3--3 of FIG. 2.

FIG. 4 is a side elevation view of the mold of FIG. 2, the mold beingrotated to a vertical position.

FIG. 5 is a partial cross-sectional representation taken along line 5--5of FIG. 1, a wooden base plate being added thereto to illustrate the useof the anchor bolts of the panel.

FIG. 6 is an enlarged representation of a corner of the panel of FIG. 1shown attached to an adjacent similar panel.

FIG. 7 is an enlarged partial representation of the panel of FIG. 1showing a corner thereof welded to a mounting plate carried by abuilding foundation.

FIG. 8 is a partial cross-sectional representation of the panel of FIG.1 taken along line 8--8 thereof.

FIG. 9 is a representation of the appearance of conventional pumice asseen through an electronic microscope.

FIG. 10 is a representation of the appearance of the selected pumice ofthe inventive concrete as seen through an electronic microscope.

FIG. 11 is diagramatic representation of several properties of severaltypes of concrete, including the concrete of the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Reference is made now to the drawings, wherein like numerals are used todesignate like parts throughout. FIG. 1 in particular illustrates apresently preferred embodiment of the present invention, generallydesignated 10, comprising a lightweight precast concrete modular panelespecially suitable for forming a part of a building when seriallyconnected with other similar panels. The illustrated panel 10 isgenerally rectangular in shape. However, panels of any desired shapecould be used, some of which could be configured to form openings forwindows, doors and the like, so that substantially all of the walls of adwelling or other suitable building could be formed by serial connectionof the panels.

The panel 10 comprises a first layer 12 of lightweight concrete and asecond layer 14 of a second lightweight concrete. The layers 12 and 14each comprise concrete made from mixes comprising aggregate selected toimpart particular desirable characteristics to the panel 10, saidcharacteristics varying between layers 12 and 14, as will be hereinaftermore fully described. For example, the layer 12 may be formulated toimpart structural strength to the panel 10, while the layer 14 may beformulated to impart a high degree of thermal insulation to the panel.

As hereinafter fully described, the concrete comprising the structurallystrong layer 12 comprises aggregates selected for their ability to vestthe concrete of layer 12 with high strength, high water resistance, lowthermal conductivity, and light weight. The aggregates comprise scoria100, pumice 102 of a particular nature hereinafter described, andchopped fiberglass 104 or other suitable fibrous material. (See FIG. 7)Both layers 12 and 14 preferably comprise such fibrous material, whichhelps to achieve a structurally sound interface between the layers 12and 14, as will be described in greater detail hereinafter.

Referring again to FIG. 1, the panel 10 may also comprise a plurality ofwelding plates 18 embedded in the concrete of the panel 10 and extendingto the corners 11, so that similar panels may be secured together bywelds 13 connecting the plates 18 of the adjacent panels together toform a wall or the like. (See FIG. 5) The plates 18 may also be secured,by welds 15, to suitable foundation plates 26 carried by a suitablefoundation 28, as seen in FIG. 6. The panel 10 may also have anchorbolts 25 cast into the body of the panel 10 and having extendingthreaded portions 27. The anchor bolts 25 may be used to connect thepanel 10 to other structural components of a building of which the panel10 may become a part. See FIG. 7, which, for example, illustrates theuse of the anchor bolts 25 to secure a wooden mounting plate 29 to a topsurface 31 of the precast panel 10. Ceiling joists or the like, notshown, may then in turn be secured to the mounting piece 29 duringconstruction of the building.

The panel 10 may also carry electrical outlet boxes 20 withcommunicating electrical wiring conduits 21. As best seen in FIG. 8, theoutlet boxes 20 may be cast into the panel 10 so as to present an openside 23 thereof flush with a surface 33 of the panel 10, so that accessto the box 20 is provided for installation of electrical wiring, notshown. Each box 20 carries communicating conduits 21, which may be sodisposed in a preplanned manner so that the conduits 21 will communicatewith corresponding conduits in adjacent modular panels when the panels10 are used to form the wall of a building, or with the top surface 31of the panel 10. Thus, the electrical wiring of the building may beinstalled without subsequent installation and mounting of conduits in oron the walls thereof.

The panel 10 may also carry one or more layers of wire mesh 16 embeddedin one or both of the layers 12 and 14, to impart additional compressiveand tensile strength to the panel 10. The mesh 16 preferrably comprisesstrands 17 electrically welded at their junctures 13. The mesh 16preferably extends substantially the full extent of the panel 10.

The use of precast modular panels to form the walls of a building has ageneral potential economic advantage, since mass production methods maybe employed in a facility for that purpose, so that the panels may beconstructed and installed with a total savings in labor cost. However,the degree to which this potential economic advantage can be exploitedis dependent upon several characteristics of the panels themselves.Thus, panels should desirably exhibit high resistance to the flow ofheat, so that thin panels may be used without subsequent excessive costsin heating and cooling of the building in which the panels are used.Further, the panels should have high structural strength, so that highlyinsulative panels may be constructed thinly so as to exploit the highinsulative properties without being so weak as to present a problem inhandling during their installation, or from imposed building loads, andloads from wind, snow and the like.

Panels of both high insulating and high strength characteristics may beconstructed of lighter weight so that they may be handled more easilyand with less expensive lifting equipment and the like. As hereinafterfully described, the panel 10 is constructed of materials which impartimproved insulating properties and improved structural strength so thatthe full economic advantage of a lightweight, highly insulative, andstructurally strong modular building panel may in fact be exploited.That is, the present invention makes possible the construction ofprecast concrete modular panels exhibiting lower weight than do presentprecast panels, while maintaining standards of strength and thermalconductivity. Or, stated conversely, the present invention enables theconstruction of panels of the same weight as present panels, whileexhibiting improved structural strength and thermal conductivity.

COMPOSITION, STRENGTH AND WATER RESISTANCE

As previously indicated, the embodiment of the panel 10 illustrated inFIG. 1 comprises two layers 12 and 14 of lightweight concrete. The layer14 may be selected to impart particularly high resistance to heat flowthrough the panel 10, with the layer 12 used to impart structuralstrength to the panel 10 for its handling and use as a building panel.Further, the layer 12 itself also has unusually good thermal insulatingproperties, so that the resultant total panel 10 is both unusuallystrong and unusually high in insulating properties.

The layer 14 concrete may comprise perlite aggregate 106, which concretetypically exhibits compressive strength in the range of only 300 to 1000pounds per square inch (hereinafter p.s.i.), not sufficient forstructural use in the panel 10. Perlite concretes are thereforetypically used for insulating and not for structural purposes. Perliteis a volcanic glass generally broken by concentric cracks formed bycooling upon its formation, made up of small spheroidal masses. It maybe expanded by application of heat before use as an aggregate inconcrete or plaster.

The inventive perlite concrete comprises also fibrous material, such aschopped fiberglass 104, which material further assures the sound unionof the layers 12 and 14 in the finished panel 10. Vermiculite, pumice(conventional or selected as in the layer 14) or other suitableinsulative aggregates may also be used in the layer 12, as may asuitable mixture of such lightweight insulative aggregates.

Of particular significance to the present invention is the structurallystrong lightweight concrete comprising the layer 12. The layer 12 mayoften be disposed outwardly in the building wall, so that it is subjectto attacks by moisture during the life of the building. Accordingly itis desirable that this lightweight layer 12 be resistant to theabsorption of water without compromise of its strength. It has beenfound that such a concrete can be constructed comprising scoria 100 asone aggregate therein to generally provide strength, along with selectedpumice 102 as another aggregate, the pumice 102 generally serving toimpart water resistance to the concrete.

Pumice is, in general, a highly vessicular, highly porous, volcanicglass formed by the extravasation of water vapor at high temperatures,being a glass froth typically composed of a mass of silk-like fiberswhich form many pores, so that pumice in general is so light as to floaton fresh water. Under an electronic microscope, however, conventionalpumice appears largely globular or nodular, the nodules largely formingthe macroscopic fibers. However, the selected pumice for the inventiveconcrete is stronger and more dense, and appears under an electronicmicroscope to be substantially of fibrous or crystal-like structure, asis hereinafter more fully described.

Scoria of the volcanic type is a rough vesicular cinder-like lavadeveloped by expansion of enclosed gases in volcanic magma. It isgenerally rather dark in color, and has considerable structuralstrength, although light in weight. The term "scoria" has acquiredvarious different meanings in the building art, and is most commonlyused to refer to the refuse of the reduction of ores. For purposes ofthis application, the term "scoria" is used throughout, in both thespecification and the claims, to mean "volcanic scoria" as hereinabovedescribed and defined.

Concretes comprising scoria aggregate generally exhibit strongtendencies to absorb water, rendering such concretes largelyunsatisfactory for use in exposed structures. Scoria concretes, however,exhibit structural strengths typically in the range from about 1200p.s.i. to about 3000 p.s.i., the latter being at least marginallysufficient for structural uses. (See FIG. 11)

Addition of fibrous materials, such as chopped fiberglass 104, inrelatively small amounts to scoria concretes has been found by theinventor to increase their strengths to as high as 4200 p.s.i., wellinto the range of strength of structural concretes. As hereinafter morefully described, such concretes may be readily produced with structuralstrengths of over 3000 p.s.i., entirely adequate for use in the panel10, and in building panels in general. The strength of such concretesfalls into the range bounded by lines 80 and 82 as seen in FIG. 11.

The aforementioned pumice aggregate improves the thermal conductivity ofthe layer 12 concrete, as well as imparting water resistance. However,the inventor has discovered that only pumice of a particular descriptionwill produce a sufficiently strong concrete in combination with scoria.While there is no confirmed explanatory theory, pumices from variousgeographical sources differ in ability to produce high strength scoriaconcretes. The inventor has discovered that pumices which impart thedesired strength along with water resistance may be obtained at leastfrom the vicinity of Lava Hot Springs, Idaho, from Milford, Utah, andfrom Malad, Idaho, whereas pumice from all other sources known to theinventor in the Western United States will not do so.

Further, the satisfactory pumice may be identified by examination of itsmicro-structure, using an electronic microscope. The observabledifferences in structure between the satisfactory and unsatisfactorypumice are illustrated in FIGS. 9 and 10. Referring to FIG. 9, it isseen that the structure of the unsatisfactory pumice appears under themicroscope to substantially comprise nodules 70 of microscopic size. Incontrast, the structure of the desirable pumice, as seen in FIG. 10, ischaracterized by the presence of a greater number of elongatedstructures 72, fiberlike or crystal-like in appearance, and of greatersize than the nodules 70, which may be as small as 400-500 microns. Itis speculated that the crystal-like nature is an important factor to thewater resistance properties, because it may be accompanied by fewer, andless extensive, capillary-like pores providing passages for water.However, laboratory tests of absorption capabilities of pumice of thetwo types reveal no significant differences between them. Thesestructures may also improve the strength of the pumice.

Laboratory investigations reveal no significant differences in thechemical compositions of the two types of pumice.

Both types are of volcanic glass, comprising high percentages of silicadioxide, and seem to have approximately the same minor percentages ofother materials in approximately the same proportions, being severalmetallic oxides and a small amount of water. However, laboratory testsdo show that the desirable pumice is of greater density and of greatercompressive strength, being about 90 pounds per cubic foot and about 600pounds per square inch respectively. In contrast, the unsatisfactorypumice has little structural strength to impart to the concrete. It isspeculated that the satisfactory pumice was formed in past geologicalages under conditions of greater temperature and pressure than was theunsatisfactory, weaker pumice, such conditions resulting in thediffering structures as illustrated by FIGS. 9 and 10.

The special selected pumice described above and used in the inventiveconcrete, further, fully conforms to Federal Housing AdministrationMinimum Property Standards 704-2.1 for lightweight aggregates.Accordingly, the selected pumice may be used for structural concrete indwellings built under Federal auspices. Such was the conclusion of theTechnical Standards Architecture and Engineering Division of theDepartment of Housing and Urban Development of the Federal HousingAdministration after examination of samples submitted in 1970. In fact,the inventive concrete was so used on an experimental basis in adwelling constructed by the inventor in 1970, under the auspices of theDepartment of Housing and Urban Development. Tests conducted by anindependent testing laboratory indicate that the selected pumiceaggregate has a compressive strength in the neighborhood of 600 poundsper square inch and a density of 90 pounds per cubic foot. Conventionalpumice, in contrast, has almost negligible compressive strength, a factwhich has effectively limited its use to that of insulating fillers,plasters and the like.

The present state of the art in respect to economically achievablestrengths of concretes is illustrated in FIG. 11, which showscomparative weights and strengths of concretes comprising severallightweight aggregates, as well as the strengths and weights ofstructural concretes. Structural concrete typically comprises gravel,sand or the like, being hard, dense aggregates. Note that thelightweight aggregate scoria 100 can produce lightweight concretes ofabout 80 or 90 pounds per cubic foot (p.c.f.), which exhibit structuralstrengths of as much as 3000 pounds per square inch (p.s.i.), which isat least marginally within the structural concrete range. However, theinventive concrete is not so limited in strength, being represented inFIG. 11 by the lines 80 and 82, which establish the boundaries of theproperties achieved at the present time by the inventive concrete. Notethat strengths of 3000 to 4200 p.s.i. have been achieved by theinventive concrete, which, as hereinbefore described, comprises scoria,selected pumice, and chopped fiberglass.

Note also from FIG. 11 that concrete comprising pumice 102 aggregatealone exhibits strengths of about 1000 to 1800 p.s.i. Accordingly, sincescoria concretes exhibit strengths of about 1200 to 3000 p.s.i., itwould be reasonable to expect that a lightweight concrete comprisingboth scoria and conventional pumice aggregates would exhibit strengthsof substantially less than 3000 p.s.i., perhaps below the structuralconcrete range. However, the inventive concretes typically exhibitstrengths well into the structural range, as hereinabove described,which fact may be attributed to the selected pumice and to the additionof the chopped fiberglass 104.

Note also from FIG. 11, that concretes comprising other lightweightaggregates, such as expanded slag, cinders, expanded shale, clay orslate especially treated in a rotary drying kiln, or sintered, may alsoexhibit high strengths. However, these concretes do not in general havethe resistance to moisture absorption of the inventive concrete, nor dothe cinder concretes. There is one exception, being concrete comprisingexpanded shale (going under the trade name of Utilite) or slate treatedin a rotary kiln or sintered. However, such concretes are inherentlyexpensive to produce, because of the necessary special treatment andspecial handling required for the aggregate in the mixing and curingprocess.

A typical formulation of the layer 12 concrete for use in panel 10comprises:

By Weight

51/2 bags of cement (94 lbs. each=517 lbs.)

700 lbs. of 1/4 in. aggregate (See below)

700 lbs. of fines (conventional pumice, 1/8 in.)

25 lbs. of 1/4 in. chopped fiberglass

By Volume

50% of 1/4 in. aggregate (25% scoria, 1/4 in. to 1/2 in. mesh)

50% fines (selected pumice, 1/8 in. mesh)

5 lbs. of 1/4 in. chopped fiberglass per bag of cement

51/2 bags of cement

The aggregate used in the inventive concrete typically comprises 25-30%of 1/4 inch selected pumice 102, and 25-30% of 1/4 inch to 1/2 inchscoria 104. The fines comprise 40-50% of 1/8 inch conventional pumicefines.

To produce the layer 12 concrete, the above described aggregates andcement are thoroughly mixed together in a mixer and sufficient wateradded for hydration of the cement, and to produce sufficient workabilityto the wetted mixture. The workable mixture is then poured into asuitable panel mold 30, as hereinafter described.

The strength of the inventive concrete can presently best be achievedthrough a batch mixing process. Continuous mixing approaches presentdifficulties in producing the strengths hereinbefore indicated for theinventive layer 12 concrete. This is probably only because continuousmixers do not permit observation of the thoroughness of the mixing. Itis expected that continued investigation will enable the high strengthinventive concrete to be produced by the continuous mixing process,wherein the aggregates, cement, water and the like are continuouslyadded in proper proportions into a continually operating mixingapparatus and continuously poured therefrom into the molds.

The inventive lightweight concrete for use in modular panel 10 typicallyachieves sufficient strength by curing for about five hours after beingplaced in the panel molds 30 (see FIG. 2), for their handling andtransport to a final curing location as hereinafter described. The totalcuring time required for the inventive concrete is substantially thesame as for the conventional structural concretes, being in theneighborhood of 30 hours under normal conditions. The curing times canbe accelerated by the use of steam in the batch mixer, which is ofcourse desirable to increase the capacity of a panel producing plantthrough reduced tie-up time for the panel forming molds. However, theuse of steam is not an essential element of the process for producingthe lightweight panels 10 of lightweight concrete. The detailed processby which the panels may be produced is described hereinafter.

INSULATIVE PROPERTIES

It is apparent from the information presented hereinabove that theinventive concrete is readily produced and possesses the requisitestructural strength for use in the modular panel 10 and that theconcrete is abundantly resistant to moisture and water damage. Considernow the thermal insulating properties of the panel 10. The panel 10 may,for example, comprise a layer 12 of 6 inch thickness and a layer 14 of 2inch thickness. The layer 14 concrete, comprising highly insulativeaggregates, has a low thermal conductivity, especially for a concretehaving structural strengths well into the structural range. In fact,presently available data, although limitted in amount, indicates thatthe layer 14 concrete has a thermal conductivity well below that of theavailable, weak insulating concretes such as those comprising perliteand the like. This present data indicates that the inventive layer layer14 concrete has a thermal conductivity in the neighborhood of 0.1075BTU/hr-Ft °F., whereas perlite concretes and the like typically exhibitthermal conductivities of around 0.300 BTU/hr-Ft°F. at comparablereference temperatures.

The aforesaid thermal conductivity of the layer 14 concrete wouldindicate that no layer 12 of conventional insulating concrete would beneeded in the panel 10. However, since thermal conductivity data for thelayer 14 concrete is at this time very limitted, it has been consideredadviseable to use the layer 12 of confirmed high insulative performance.The panel 10 comprising the layers 12 and 14 has exhibited insulatingproperties heretofor achieved in concrete panels of comparablethicknesses only by the addition of substantially thick layers ofinsulating layers of cork, cellular plastic sheets, wood and the like,after such panels are cast and cured.

It is therefore apparent that the modular panel 10 is outstanding ininsulating properties, while also providing the requisite structuralstrength and water resistance.

OTHER PANEL CHARACTERISTICS

The modular panel 10 inherently has several characteristics improvingthe economy of construction of buildings, because of certain generalcharacteristics of pumice and perlite concretes retained by theinventive concrete. Nails may be driven directly into such concreteswith an ordinary carpenter hammer and ordinary nails without drillingpreparatory holes. Also, the perlite concrete can accept an interiordecorative plaster, if desired, directly on its surface. Further, eitherof the perlite and the scoria-pumice concrete surfaces may be texturedby the use of texturing layers in the molds 30 in which the panels 10are formed. Thus, popcorn, simulated wood grain finishes and the likemay be achieved during the manufacture of the panels 10 with negligibleadditional expense, saving the entire cost of final surface finishing ofthe panels after their erection.

METHOD OF MANUFACTURING

A presently preferred method of manufacturing the modular panel 10 isnow described with particular reference to FIGS. 1-4. FIG. 2 is aperspective representation of a horizontally disposed mold, generallydesignated 30, defining the four edges and one side of a rectangularpanel 10. Panel mold 30 has a bottom plate 32, side plates 34, and endplates 36 and 38, all of said plates being removably secured together bysuitable fasteners or the like, not shown. The bottom plate 32 mayoptionally be overlaid with a mat 40 having an upwardly disposed surface42 textured to impart a pleasing surface appearance to the finishedpanel 10.

While only a single panel mold 30 is illustrated in the Figures, itshould be understood that a plurality of such molds could be used, sothat large batches of panel forming concrete, or a continuously suppliedmixture from a continuous mixer, could be used in a single pour so as toproduce a plurality of the panels 10.

The welding plates 18 may be disposed in the mold 30, as best seen inFIG. 2, as may be strengthening wire mesh 16. The anchor bolts 25 aredisposed in bores 37 in the end plates 36 and 38, with threaded ends 27extending to the exterior of the mold 30. Electrical receptacle boxes 20and the associated electrical conduits 21 may be suitably supported inthe mold 30, as shown in FIG. 3 and in more detail in FIG. 10. The mesh16 may be utilized to support the boxes 30 using wire ties 39, so thatthe open end 23 thereof communicates with a surface 33 of the panel 10.The open boxes 20 may be filled with wadded paper or the like, notshown, to preclude the entry of concrete thereinto during pouring of theconcrete comprising the panel 10 into the mold 30.

The mold 30 carries an axle 44 secured to the bottom plate 32 by welds53, as best seen in FIG. 3. The axle 44 communicates pivotally with moldsupports 48 through bores 46 therethrough. Fixed supports 50 areprovided also, so that the mold 30 rests in the horizontal position asseen in FIGS. 2 and 3.

After the mold 30 is assembled, and the wire mesh 16, boxes 20, and thelike are installed therein as seen in FIG. 2, a first quantity ofconcrete is poured to form the layer 12 in the bottom of the mold 30 toits designated thickness in the finished panel 10 and the mold 30 isvibrated by any suitable vibrator a sufficient time to cause the uncuredconcrete to completely fill the mold 30 and to efficiently entrain thepreviously described objects therein. The layer 12 comprises thescoria/pumice, fiberglass inventive concrete, the formulation and batchmixing of which is hereinbefore described.

After the layer 12 is thus formed in the mold 30, the layer 14,comprising the insulative concrete hereinbefore described, isimmediately poured into the mold 30 onto the layer 12, while layer 12 isstill uncured, and the mold 30 is vibrated a few seconds to form athoroughly intermixed interface between the layers 12 and 14, so thatthe panel 10 will be entirely monolithic after its cure, said monolithicstate being assured by the fibers carried by both layers 12 and 14. Theupper surface 33 of layer 14 is then trowelled.

After the second layer 14 is poured and the mold 30 vibrated briefly,and the surface 33 trowelled, both layers 12 and 14 are allowed to curetogether a suitable period of time, typically about five hours, for theconcrete to achieve an initial partial amount of structural strength.After this period, the end plates 36 and 38 are removed from the mold30, and are replaced by corresponding lifting plates 54 and 56, as seenin FIG. 3. The lifting plates 54 and 56 carry bores 57 therethroughaccepting the anchor bolts 25, so that the plates 54 and 56 may besecured to the partially cured panel 10 by nuts 58 engaging the threadsthereon. The lifting plates 54 and 56 carry also lifting hooks 60 and 62respectively.

Cable 59, carried by any suitable crane or other lifting device, notshown, is then used to engage the hook 60 to pivot the mold 30 about theaxle 44, carrying the panel 10 into a vertical position (See FIG. 4),and to lift it from the mold 30 onto a suitable carrier for transport toa suitable final curing station for completion of cure. The mold 30, nowbeing relieved of the partially cured panel 10, may now be immediatelycleaned as necessary, reassembled, and used for a next pouring of a nextpanel 10.

After completion of cure of the panel 10 in the above mentioned curingstation, the panel 10 may be suitably stored for later use, orimmediately transported to a building site for immediate installation asa portion of the wall of a building, as hereinbefore described.

The details of the design of the panel 10 may be varied as required forparticular applications without departing from the spirit of the presentinvention, as may the process of manufacturing described herein. Forexample, some applications may not require the insulating layer 12, suchas those wherein the panel may be used for interior walls, or for thefloors of a building. In some applications, it may be desirable to usetwo insulating layers 14 disposed on the opposite sides of thestructurally strong layer 12. Also, the panel 10 as described hereincould as well be produced by pouring the insulating layer 14 prior tothe structural layer 12, so that a decorative textured surface could beprovided thereon by a textured mat disposed in the bottom of the mold30. And, as previously indicated, the mold 30 could be shaped so thatthe panel 10 would carry openings and mounting hardware for windows,doors and the like.

The embodiments of the present invention described herein are intendedto be illustrative only, and not restrictive. The scope of the presentinvention and the boundaries thereof are intended to be as defined bythe appended claims, and all embodiments, processes, and methodscontained therein are intended to be embraced thereby. The inventionaccordingly may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. All changes whichcome within the meaning and range of equivalency of the appended claimsare intended to be embraced therein.

What is claimed and desired to be protected by United States LettersPatent is:
 1. A precast modular panel for forming at least a portion ofa building, comprising:at least one layer of lightweight concretesubstantially the full extent of the panel, comprising volcanic scoria,a suitable fibrous material, and pumice, the pumice being of a typehaving a microstructure substantial portions of which appear fiber-likeunder an electronic microscope, said type being found at least in thevicinity of Milford, Utah, Malad, Idaho, and Lava Hot Springs, Idaho, sothat the volcanic scoria, the fibrous material and the pumice cooperatetogether in the concrete to render the layer structurally strong andresistant to water.
 2. The panel of claim 1 wherein:the fibrous materialis chopped fiberglass.
 3. (a) A precast modular panel for forming atleast a portion of a building, comprising:at least one layer oflightweight concrete substantially the full extent of the panel,comprising volcanic scoria, a suitable fibrous material, and pumice, thepumice being of a type having a microstructure substantial portions ofwhich appear fiber-like under an electronic microscope, said type beingfound at least in the vicinity of Milford, Utah, Malad, Idaho, and LavaHot Springs, Idaho, so that the volcanic scoria, the fibrous materialand the pumice cooperate together in the concrete to render the layerstructurally strong and resistant to water, and at least one additionallayer of lightweight concrete substantially the full extent of thepanel, comprising aggregates selected from among perlite, vermiculite,and a suitable mixture of vermiculite and perlite, and a suitablefibrous material, so that the insulating properties of the panel areenhanced and the layers are bonded permanently together upon cure afterthe layers are successively poured into a mold one upon the other. 4.The panel of claim 3 wherein:the fibrous material is chopped fiberglass.5. The panel of claim 3 further comprising:at least one layer of wiremesh embedded in the concrete of the panel so as to impart additionalstructural strength to the panel.